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Chapter 11: Dynamic Analysis
Omar Meqdadi
SE 3860 Lecture 11Department of Computer Science and Software Engineering
University of Wisconsin-Platteville
2
Topic Covered
Why Dynamic Analysis Control Flow Trace Dynamic Dependence Graph Dynamic Backward Slicing
3
Dynamic Analysis
Dynamic analysis : dynamic representations of the code determine a flow through a software system given a
particular set of inputs or a user scenario(s). Part of the impact analysis of required change Why
Help maintainer gain initial understanding of a software system
Diagnose and/or localize problems. Static analysis is very imprecise
Example: Debugger
Dynamic Analysis
Dynamic program representations Control Flow Trace Dynamic Dependence Graph
Control Flow Trace
List of all the execution points (execution paths) given a particular program point (input)
Flow chart when executing a given input Format :
<… xi, …> , where xi is an execution point
Steps: Draw the flow chart Find the execution given a particular input
Control Flow Trace: Example
3: while ( i<N) do
1: sum=02: i=1
4: i=i+15: sum=sum+i
6: print (sum)
11: sum=0
31: while ( i<N) do
51: sum=sum+i32: while ( i<N) do 42: i=i+1
33: while ( i<N) do 61: print (sum)
N=3:
21: i=1
41: i=i+1
52: sum=sum+i
Flow Chart Control Flow Trace at N=3
N = 3 : < 11, 21, 31, 41, 51, 32, 42, 52, 33, 61 >
Dynamic Dependence Graph
Dynamic Dependency Graph (DDG) : A PDG ( see Chapter 10) assuming fixed input for the
program Reconsider the following code
from Chapter 10 and assume
X( from statement S1) = -1:
DDG Example
PDG DDG at X = -1
Dynamic Backward Slicing
Recall that program slice is a subset of a program that contains the relevant code to the computation of interest, see Chapter 10.
Dynamic Slicing assumes fixed input for a program A dynamic backward slice query is S < V , I , N >
The set of statements involved in computing variable V’s value at statement N assuming that I is the input for the program
Advantages : Smaller More precise More helpful to the user
Dynamic Backward Slicing
Two Approaches: Considering only the data dependency (Minimal Slicing)
Using Dynamic Data Dependency Graph Considering both data and control dependencies
Using Dynamic Dependency Graph
1: b=02: a=23: for i= 1 to N do4: if ((i++)%2==1) then5: a = a+1 else6: b = a*2 endif done7: z = a+b8: print(z)
S < z , N=2, 8 >11: b=0 [b=0]
21: a=2
31: for i = 1 to N do [i=1]
41: if ( (i++) %2 == 1) then [i=1]
51: a=a+1 [a=3]
32: for i=1 to N do [i=2]
42: if ( i%2 == 1) then [i=2]
61: b=a*2 [b=6]
71: z=a+b [z=9]
81: print(z) [z=9]
Dynamic Backward Slicing Approch1:
Dynamic Backward Slicing Approach2
Using DDG: A dynamic program slice is identified from a DDG as follows:
for a variable V at node N, identify all reaching definitions of V.
find all nodes in the DDG which are reachable from those nodes.
The visited nodes in the traversal process constitute the desired slice.
Consider the program in the slide 7 and variable Y at S10. Therefore, with respect to variable Y at S10, the dynamic slice will
contain only {S1, S2 and S3}. So: For −1 as the values of X, if the value of Y is incorrect at S10,
one can infer that either erroneous at S3 or the “if” condition at S2 is incorrect.